Database ZF (ZERMELO-FRAENKEL) SET THEORY ZF Set Theory - add the Axiom of Infinity Well-Founded Induction frins2  
				
		 
		
			
		 
		Description:   Well-Founded Induction schema, using implicit substitution.
       (Contributed by Scott Fenton , 8-Feb-2011)   (Revised by Mario Carneiro , 26-Jun-2015) 
		
			
				
					Ref 
					Expression 
				 
					
						Hypotheses 
						frins2.1    ⊢   y  ∈  A    →    ∀  z  ∈   Pred  R  A  y    ψ     →   φ         
					 
					
						frins2.3    ⊢   y  =  z    →    φ   ↔   ψ         
					 
				
					Assertion 
					frins2    ⊢    R  Fr  A    ∧   R  Se  A     →   ∀  y  ∈  A   φ          
				 
			
		 
		
				Proof 
				
					
						Step 
						Hyp 
						Ref 
						Expression 
					 
						
							1 
								
							 
							frins2.1   ⊢   y  ∈  A    →    ∀  z  ∈   Pred  R  A  y    ψ     →   φ         
						
							2 
								
							 
							frins2.3   ⊢   y  =  z    →    φ   ↔   ψ         
						
							3 
								
							 
							nfv  ⊢   Ⅎ  y   ψ        
						
							4 
								1  3  2 
							 
							frins2f   ⊢    R  Fr  A    ∧   R  Se  A     →   ∀  y  ∈  A   φ